Automotive vacuum pumps are used to provide a vacuum of an absolute pressure between 100 mbar and 1 mbar as an actuation vacuum for switches, servo brake actuators etc. In contrast to a volumetric vacuum pump without oil-lubrication, an oil-lubricated vacuum pump has reduced frictional losses, reduced wear and, due to a better pneumatic isolation of the rotating pump chambers, an increased pump efficiency.
The discharge of the air and the oil at the end of the discharge phase can, however, be critical if a substantial volume of oil is still present in the rotating pump chamber. If the oil is not completely discharged in the discharge phase and is therefore compressed, a high pressure load at the vane head and an increase of the power consumption can result.